This invention relates to an electrochemical process for the decomposition of hydrogen sulfide including the anodic oxidation of sulfides and cathodic reduction and evolution of hydrogen.
The removal of hydrogen sulfide from gaseous streams is a problem that has long challenged many areas of industry. It has been a particular problem in the petroleum industry which produces large quantities of hydrogen sulfide.
Over the years, much research has been directed towards electrolysis of hydrogen sulfide. While many advances have been achieved, significant problems remain in commercializing the process. Typically, electrolysis of liquid hydrogen sulfide suffers from poor conductivity and containment problems. Use of an aqueous medium resolves many issues, but if accompanied by sulfur fouling of the anode, side product formation in strongly alkali medium, and low hydrogen sulfide loading in the acid medium.
Chang et al. U.S. Pat. No. 4,765,873 describes a process for removing hydrogen sulfide from a gaseous stream by contacting the stream with an aqueous solution of ammonium hydroxide to produce ammonium sulfide. This ammonium sulfide is then converted to an ammonium polysulfide intermediate in an electrolytic cell. Thereafter, the ammonium polysulfide is oxidized to sulfur in a heating zone utilizing an oxygen containing gas sparge.
Another method for decomposition and removal of hydrogen sulfide into hydrogen and sulfur is described in Joshi, U.S. Pat. No. 5,578,189. In this process, a gas containing the hydrogen sulfide is contacted with a solid metal ion conducting electrolyte in which the metal is a sulfide forming metal under metal ion conducting conditions to react the metal with hydrogen sulfide under metal sulfiding conditions. A hydrogen sulfide free gas is recovered containing hydrogen and the metal sulfide is electrolytically converted to reform the metal and recover sulfur.
In Winick, U.S. Pat. No. 4,772,366, hydrogen sulfide is removed from a gas mixture by providing an electrochemical cell with a porous cathode and porous anode. This cell is provided with an aqueous electrolyte and a gas mixture containing H.sub.2 S is directed into contact with the cathode to cause reduction of the H.sub.2 S to polysulfide ions. These polysulfide ions are allowed to migrate from the cathode and concentrate at the anode.
A process involving the electrochemical oxidation of hydrogen sulfide is described in Bolmer, U.S. Pat. No. 3,249,522. That process is specifically developed for the operation of a fuel cell in which the hydrogen sulfide is employed as the fuel. That process uses a sulfur solvent which is vapourizable under process conditions.
It is the object of the present invention to provide an electrolytic process for decomposing hydrogen sulfide in which soluble polysulfide would be produced, thereby avoiding fouling of the anode.